Variable-speed drive for compressors



y l948- w. E. TRUMPLER VARIABLE SPEED DRIVE FOR COMPRESSORS Filed Jan. 15, 1945 INVENTOR.

Patented May 18, 1948 VARIABLE-SPEED DRIVE FOR COMPRESSORS William E. Trumpler, Olean, N. Y., assignor to Carrier Corporation, Syracuse, N. Y., a corporation of Delaware Application mum-15, 1945, Serial No. 572,869 s Claims. (01. 230-11) 1 This invention affords the advantages flowing from the use of a variable speed drive more particularly for refrigerant compressors.

It relates to a drive arrangement more particularly for a compressor of the centrifugal type,

and is directed in the field of refrigeration to the use of an auxiliary turbine-compressor unit for providing a variable speed-up drive for a primary refrigerant compressor.

In providing. variable speed electric motor direct drive for a primary compressor, certain disadvantages arise. The efficiency of the motor is appreciably reduced as the speed is reduced; and the provision of a variable speed motor, together with the controls for obtaining a practical range of speed, in many cases, is uneconomic and is always more costly than the use of a constant speed motor.

In addition, the use of a direct-connected motor for driving a primary compressor at a number of different speeds requires an intermediate gear or speed step-up arrangement which again adds to the cost and involves other disadvantages.-

It is the general object to provide an auxiliary turbine-compressor unit, the compressor of which is driven by a constant speed motor. Refrigerant or other gas will be employed substantially in a continuous cycle in the turbine-compressor unit. The compressor will drive, pneumatically, the turbine at a desired speed and the turbine will, in turn, drive a primary compressor connected thereto. In practice, where the primary compressor is a centrifugal refrigerant compressor, I provide means for feeding refrigerant from the discharge of the last stage of said primary compressor to an intake port, preferably at the intake of the compressor of the compressorturbine combination. Refrigerant from the disv charge side of the compressor of said unit will, in

such case, be returned to the intake side of the primary compressor. Regulating valves governing the admission and return of such refrigerant pressor. Assuming it is desired to maintain a constant water temperature, the valves will be opened and closed, as hereinafter explained, as the water temperature in the cooler tends to vary.

For example, upon an increase in load reflected by admin water temperature, the primary compressor will normally require more power. However, if the power delivered by the compressor element of the turbine-compressor unit remained the same, then the turbine and the primary compressor would slow down as a result. Contrary to this natural action, the control responsive to water temperature raises the density level of gas in the unit, thereby increasing the power output of the compressor of the unit which in turn results in a rise rather than a drop of speed of the unit will similarly bring about a desired variation in the speed of the primary compressor to compensate for the change in loading.

will desirably vary the density level of refrigerant vapor admitted to the unit. The compressor of gas from the primaryv compressor to the unit may be'regulated responsive to changes in water tem- -perature of a cooler served by the primary comvalves for admitting and returning refrigerant It will be understood, of course, that instead of refrigerant gas, other fluid gasesmay be used for driving the compressor of the unit which, in turn, will cause the turbine of the unit to provide more or less power, as desired, to the shaft of any compressor, or similar apparatus to be driven.

Other features will be apparent from the following description of one form of the invention to be read in connection with the accompanying drawings showing a diagrammatic arrangement of a primary compressor served by a combination turbine-compressor unit, the compressor of which is driven by a constant speed motor or the like.

Considering the drawings, numeral 2 refers to the casing of a refrigerant compressor of the Carrier centrifugal refrigeration type. As is known in the art, such a compressor is operatlvely associated with a condenser, evaporator and necessary auxiliaries to constitute a refrigeration system. For purposes of illustrating this invention, only the compressor, evaporator in part, and associated elements will be shown.

Within the casing 2. are arranged stages 3, 4

and 5, representing three stages of compression.

It will be understood that any number of stages may be employed, depending upon the'capacity required and application for which the machine is designed. Each stage contains animpeller 6 for compressing in series a suitable refrigerant admitted through inlet 1. The refrigerant gas is discharged from the last stage of compression and is routed through a volute 8 to a condenser. The impellerst are driven by the main shaft 9 of the primary.compres'sor generally identified by numeral llif Shaft 9 is suitably mounted on bearings in housing H, the shaft having an extension I2 holding a turbine wheel as hereinafter described by a key and suitably locked by nut l3 within turbine portion l4 comprising one part of turbine-compressor unit l5. Numeral l6 designates the compressor portion of unit i5. The casing 2 is designed to enclose the primary compressor I and the unit l5, so that, in effect, a single housing encloses both elements. Flange portions H are provided for bolting together casing 2 and easing I8 provided for enclosing driving motor l9. Shaft of motor i9 is suitably keyed within and locked by nut 2i within compressor IS.

The turbine-compressor unit it consists of compressor portion it which includes compressor impeller 22. Gas compressed by the impeller, as

shown by the solid arrow, enters annular pas sageway 23 and then proceeds through guide vanes 24, as shown by the broken arrow, to turbine wheel 25 of turbine M, the gas leaving the turbine, as shown by the double arrow, for return to the compressor I6.

Under practical operating conditions, the compressor I6 is driven by motor it at a prescribed constant speed. The compressed gas delivered into turbine ill will cause the turbine to operate at a prescribed speed and power when gas of a prescribed density is handled by the compressor. However, when the density is increased and all other load and operating factors remain equal, the power delivered to the turbine will be increased with a consequent increase in speed of the turbine. Since the primary compressor it is directly connected to turbine it, an increase in turbine speed, other factors remaining equal, will result in a corresponding increase in primary compressor speed.

Since load and operating factors normally vary under different operating conditions, it is necessary to compensate for such variations in conditions by varying the speed of the primary compressor. Conversely, it may be desirable to operate the primary compressor at a constant speed despite operating conditions which tend to vary such speed. I may maintain a, constant speed or vary the speed of the primary compressor as may be necessary to produce ormaintain desired operating conditions.

To accomplish such control, I provide a conduit 26 connecting the discharge from primary compressor l0 preferably to a minimum pressure area 21 at the entrance to impeller 22 of compressor l6.

A second conduit 28 connects the inlet of primary compressor [0 preferably to a higher pressure area 29 adjacent turbine wheel 25 of turbine l4. Control valves 30, 3| are respectively positioned in conduits 26, 28. Valve 30 is a direct acting valve while 3! is a reverse acting valve so that as valve 30 tends to open, valve 3| will tend to close and vice versa. The valves may be controlled electrically, pneumatically, or otherwise, responsive to varying load or operating conditions reflected in an area served by the system or responsive to varying evaporator or condenser conditions, or otherwise. For purposes of illustration, evaporator 32 served by primary compressor l0 and forming part of a refrigeration system with compressor III has a liquid line 33 discharging'liquid cooled by the evaporator. The temperature of liquid in line 33 reflects changes in load conditions imposed upon the refrigerew tion system or changes in, operating conditions which may vary the power and efficiency of the system. A thermal bulb 34 reflecting changes in temperature of the liquid leaving evaporator 32 serves to control the functioning of valves 30, 3|. Thus, upon an increase in load, valve 30 will tend to open while valve 3| will tend to close. As a result, a greater weight of gas will be admitted to and be handled by compressor IS with the result that the power delivered to turbine l4 will be increased and the speed thereof increased. On the other hand, should the temperature of liquid leaving evaporator 32 drop below a desired point, then bulb 34 reflecting this drop will cause valve to tend to close and valve 3| to tend to open. In consequence the density or weight of gas then handled by compressor It will drop and the power delivered by the compressor to the turbine will accordingly decrease and the speed of the turbine decrease.

By suitable means, preferably evaporatlve coolin means employing condensate from the refrigeration system served by primary compressor iii, the turbine compressor unit may suitably be cooled and kept at a desirable temperature.

Thus, I provide a simple arrangement for varying or maintaining constant the speed of a primary compressor or similar driven element while employing as a primary source of power a constant speed motor or the like. The use of a compressor-turbine unit between such a motor and the primary compressor makes for maximum flexibility with ease of control. The use of-unsatis factory gears and expensive variable speed controls for the motor are completely eliminated and the range of variable speed service of the compressor increased to a practical maximum degree.

The primary compressor itself serves to control the operation of the compressor-turbine unit responsive to changing load or operating conditions affecting the efllciency or speed of the compressor.

I claim:

1. A speed control arrangement of the character described comprising a primary compressor, a unit consisting of a turbine portion and a com,- pressor portion combined to operate in such manner that gas is compressed by the compressor portion and delivered therefrom to the turbine portion, a motor for driving the compressor portion, a first conduit for admitting gas from the primary compressor to said unit, a second conduit connecting said primary compressor with said unit to discharge gas from said unit to said primary compressor and means for controlling the admission of gas to and discharge of gas from said unit.

2. A speed control arrangement for a centrifugal refrigerant compressor including a primary refrigerant compressor, a shaft for said compressor, a turbine compressor unit comprising a turbine portion and a compressor portion, the shaft of said primary compressor being connected to the turbine portion of the unit, a motor, a shaft for said motor, said motor shaft being connected to the compressor portion of said unit, a connection between the primary compressor and the unit for admitting gas from the primary said unit for compressor to said unit, and a second connection between the primary compressor and the unit to discharge gas from the unit to said primary compressor.

3. A control arrangement in accordance with claim 2 including means for varying the amount of gas flowing between the compressor and the unit in accordance with variations in operating conditions tending to affect the speed of the primary compressor.

4. A variable speed drive arrangement of the character described including a primary com-.

pressor, a turbine-compressor unit, a constant speed motor for driving the compressor of said unit, means associated with the compressor of said unit for driving the turbine of said unit, means directly connecting the turbine of the unit with the primary compressor, a conduit connecting the primary compressor with the intake of the unit compressor, a second conduit connecting the turbine with the intake of the primary compressor, valves in said conduits, and means for opening and closing said valves in response to variation in load imposed upon the primary compressor, said first valve in response to an increase in load tending to open to admit a greater weight n of gas to said unit compressor while said second valve tends to close thereby increasing the power delivered by the unit compressor to the turbine, while in response to a decrease in load said second valve tends to open and the first valve tends to close permitting the removal of a greater weight of gas from said unit thereby decreasing the power delivered by the unit compressor to the turbine. Y

5. A variable speed drive arrangement of the character described including a primary compressor, a turbine-compressor unit, a constant speed motor for driving the compressor of said unit, means associated with the compressor of rivingvthe turbine of said unit, means associated with the turbine of said unit for driving the primary compressor, a connection between the primary compressor and the unit for admitting gas from the primary compressor to the unit, a second connection between the primary compressor and the unit to discharge gas from the unit to the primary condenser, and means for regulating the admission of gas to and the discharge of gas from the-unit whereby the density of gas handled by the compressor of the primary condenser whereby the speed of the turbine of the unit may be varied to vary the speed of the refrigerant compressor.

'7. A variable speed arrangementof the character described comprising a primary apparatus adapted to be driven at variable speeds, a turbine-compressor unit, driving means for the compressor of the unit, a connection between the primary apparatus and the unit to admit fluid from the primary apparatus to the unit, a second connection between the primary apparatus and the unit to permit discharge of gas from the unit to the primary apparatus and means for regulating the admission of fluid to and the discharge of fluid from the unit whereby the power supplied by the compressor of the unit may be varied to vary the speed of the turbine of the unit.

8. A variable speed drive arrangement of the character described including a primary compressor, a turbine-compressor unit, means for driving the compressor of said unit, means associated with the compressor of said unit for driving the turbine of said unit, means associated with the turbine of said unit for driving the primary compressor, a connection between the primary compressor and the unit for admitting gas from the primary compressor to the unit and means permitting discharge of gas from the unit.

WILLIAM E. 'I'RUMPLER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,939,156 Wright Dec. 12, 1933 2,137,139 Keller Nov. 15, 1938 FOREIGN PATENTS v Number Country Date 361,889 Great Britain Nov. 16, 1931 unit is varied to vary the speed and power of the primary compressor.

6. A variable speed arrangement for govern.-

675,882 Germany May 20, 1939 

